[Dknits782]

hey i recently just purchased a 1990 mustang gt 5.0. My first mustang always been a subaru guy but very happy with my purchase. my question is the car is completely catless and i have a huge hole in my muffler (car came from the coast), question is can i run with my mufflers off? i will be buying new mufflers but i just started school again and im super poor. Sounds like crap with them off but better than with them on with a hole. I know with my subaru i need the back pressure but what i have read v8 are different. So will running with no mufflers or cats harm my engine, also its not tuned. I would appreciate any info u guys have to offer.

[Dap1991]

you can run it with them off it just wont sound good like you mentioned, it shouldnt need tuned unless you mean a tune up? or if it has alot of mods

[Chris951]

Backpressure is bad anyways. But yes, you can run it without mufflers.

[1988 convertible]

Originally Posted by Dknits782 hey i recently just purchased a 1990 mustang gt 5.0. My first mustang always been a subaru guy but very happy with my purchase. my question is the car is completely catless and i have a huge hole in my muffler (car came from the coast), question is can i run with my mufflers off? i will be buying new mufflers but i just started school again and im super poor. Sounds like crap with them off but better than with them on with a hole. I know with my subaru i need the back pressure but what i have read v8 are different. So will running with no mufflers or cats harm my engine, also its not tuned. I would appreciate any info u guys have to offer.

the car will run rich so be careful... some small block V8's do require certain levels of back pressure from the exhaust system despite what some people may claim so do not be fooled...

just be careful you gont get pulled by 5.0 for "excessive noise pollution", personally i would run it with the mufflers until i could afford some 2nd hand ones in better condition...

cheap and simple option instead of a whole new system would be a set of mac pro dumps:
1986-95 Mustang 5.0L 2.5" Mac Perfromance Pro Dump Exhaust System at LRS - Same Day Shipping!

[Dknits782]

I guess I will just leave the mufflers on I don't want to risk it. Only mods are a bbk intake bbk headers and h pipe also has cams nothing to aggressive. Just sucks to listen to but I guess either way sounds like crap

[Stdyhand]

It may sound like crap with a hole in the muffler but it's still quieter than running without them and they will fine you for the noise. It isn't worth it.

[fogged306]

Originally Posted by 1988 convertible the car will run rich so be careful... some small block V8's do require certain levels of back pressure from the exhaust system despite what some people may claim so do not be fooled...

This is not true. Backpressure only hinders the engine. If you go too big for your set-up in primaries and collector size, you can hurt scavenging, which is what you want, not backpressure.

Read this if you don't believe. http://www.veryuseful.com/mustang/te...Scavenging.pdf

[nolife]

Originally Posted by 1988 convertible the car will run rich so be careful...

The exhaust and back pressure is not a consideration in the closed loop operation of the computer. The 02 sensors will be able to adjust and maintain the proper A/F with no problems. Some people have the entire stock restrictive exhaust installed and others have full length headers, no cats and a 3 in pipes, many people are in between. None of them have A/F ratio problems because of different back pressures because the computer compensates for a wide variety of conditions. Taking off a muffler is not some dramatic change that screws things up. That being said... With any changes in your exhaust, you can cause some changes with low end torque or high end HP that may or may not be desirable but your A/F ratio will still be dead on and "safe" the whole time.

[Dknits782]

it seems like everyone has a different opinion on this. I pretty sure im just going to leave the mufflers on, but just curious has any one here actually ran with them off for an extended period of time with no problems? Thank u guys for the fast answers its nice to have a place to go with questions.

[1988 convertible]

Originally Posted by fogged306 This is not true. Backpressure only hinders the engine. If you go too big for your set-up in primaries and collector size, you can hurt scavenging, which is what you want, not backpressure. some small block V8's

not all... if you go too loose with your setup you will lower your torque output and screw your accelleration. this advice is for an engine with a stock (or near stock) set up...

this guy is a student and does not have the money to mess about modding his engine and putting a new highflow system on...

my answers to questions only ever apply to a persons situation as most set ups will be different...

for example i have a straight though system with custom chrome repackable race cans at the end similar to an S197 but this is my own custom exhaust design which can be modified 10 ways for HP/torque, sound etc with complete replacement centre pipes, mufflers, tips and so forth...

every engine is different in some aspect so dont believe everything you read about the "back pressure" argument although certain arguments are valid but only really apply to high output motors but im rambling now so will stop...

lets just say agree to disagree

[fogged306]

Originally Posted by nolife The exhaust and back pressure is not a consideration in the closed loop operation of the computer. The 02 sensors will be able to adjust and maintain the proper A/F with no problems. Some people have the entire stock restrictive exhaust installed and others have full length headers, no cats and a 3 in pipes, many people are in between. None of them have A/F ratio problems because of different back pressures because the computer compensates for a wide variety of conditions. Taking off a muffler is not some dramatic change that screws things up. That being said... With any changes in your exhaust, you can cause some changes with low end torque or high end HP that may or may not be desirable but your A/F ratio will still be dead on and "safe" the whole time.

I agree with this in the case of shorties. Although 1988 convertible is mis-informed when he says that it will make you rich, There's some truth to that, just not in the fact that any exhaust will make you run richer. Only on longtubes and not every time, but depending on the distance away from the exhaust port on the head, the O2 sensor can be too far away from it and not get enough heat from the exhaust gasses to work properly. In stock form, the computer will go into OL because of this and usually run on the richer side. With a tuner, there's ways around that, but I'm sure there's a lot of cases where people put longtubes on and ran richer, and that's why. Not rich enough to do any damage, but you would be able to tell through mileage, plugs, and exhaust smell.

[ryanw]

you will be to loud and and the cops will pull you over and give you a fix it ticket....lol

[LethalDosage]

You can run with the mufflers off, but Al Gore will find and kill you..


Sent from my Autoguide iPhone app

[Dknits782]

lol I live in Nevada cops don't care what we do or the sound, we don't even have emission laws where I live. Prostitution is even legal, there is a brothel 15 min from my house, so I don't see me getting a ticket anytime soon. From the sound of it besides the sound im safe with the mufflers off, but i will leave them on till i get tired of the stupid crappy sound from the passenger side of my car.

[fogged306]

Originally Posted by 1988 convertible not all... if you go too loose with your setup you will lower your torque output and screw your accelleration. this advice is for an engine with a stock (or near stock) set up... this guy is a student and does not have the money to mess about modding his engine and putting a new highflow system on... my answers to questions only ever apply to a persons situation as most set ups will be different... for example i have a straight though system with custom chrome repackable race cans at the end similar to an S197 but this is my own custom exhaust design which can be modified 10 ways for HP/torque, sound etc with complete replacement centre pipes, mufflers, tips and so forth... every engine is different in some aspect so dont believe everything you read about the "back pressure" argument although certain arguments are valid but only really apply to high output motors but im rambling now so will stop... lets just say agree to disagree

You can agree to disagree all you want. I 100% agree with you that you can go too large of a header and midpipe on a stock or close to stock set-up and that every set-up is different. But it's because of scavenging, not backpressure. Backpressure can change your powerband, but when you eliminate it and properly scavenge the exhaust gasses, you will always pick up power. Even on a stock engine with a minimal overlap cam.

[69fastback]

^^^^^^^ yep. I think I've had this same conversation with 1988 convertible before.

[nolife]

Originally Posted by Dknits782 lol I live in Nevada cops don't care what we do or the sound, we don't even have emission laws where I live.

All emissions laws are federal laws so you have them just like everyone else in the US. That being said, many areas do not have "emission police" and don't even perform annual checks. It is a budget issue. Understandably, no one wants to pay the taxes, fees, equipment and training to establish periodic testing and enforcement programs in less populated regions. Meaning... the laws are still there and apply but no one in your area is responsible for enforcing them.

[Dap1991]

you can always keep an eye out on craigslist if you arent looking already for some really cheap flowmasters or something, i see some pop up every once in a while

[Dknits782]

Oh craigslist is a good call I have not started looking yet.I ran all day with it off it sounds scary loud and the cams sound mean but I get a weird idle hold even after I reset it. Besides the idle and the god awfull exhuast smell in the car it runs great even seems to be faster.

[1988 convertible]

[QUOTE=fogged306;3951652]I agree with this in the case of shorties. Although 1988 convertible is mis-informed when he says that it will make you rich, There's some truth to that, just not in the fact that any exhaust will make you run richer. QUOTE]

I meant the car will run rich without any exhaust only straight through pipes... although the ECU will learn over time and compensate you will still smell it a bit in which case you could retard the timing back to 10-11...

Fogged306: Totally agree with you there but my point was on a near stock motor your better off keeping with the low end torque which is what i prefer even after all the mods... if he wants more hp then obviously he will do something different with his set up... like i said i have an interchangeable system and thats great for keeping your options open

ive used pypes, powerflow, flowmasters, magnex, borla, flowtech and some home made cherry bombs... i loved the flowmasters for sound and pressure, the flowtech was a bit raspy but good on HP and great on the track. At the moment im using some custom chromes and their freakin loud as funk...

I think i have an exhaust fetish LOL!!! i love playing around and getting different sounds and set ups experimenting with positive and negative flow... especially love when you can hear more air rushing into the intake as well from the neg flow...